Method and Apparatus of Forming Silicon Nitride Film

ABSTRACT

Provided is a method of forming a silicon nitride film on a surface to be processed of a target object, which includes: repeating a first process a first predetermined number of times, the process including supplying a silicon source gas containing silicon toward the surface to be processed and supplying a decomposition accelerating gas containing a material for accelerating decomposition of the silicon source gas toward the surface to be processed; performing a second process of supplying a nitriding gas containing nitrogen toward the surface to be processed a second predetermine number of times; and performing one cycle a third predetermined number of times, the one cycle being a sequence including the repetition of the first process and the performance of the second process to form the silicon nitride film on the surface to be processed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Application Nos.2013-210456 and 2014-170202, filed on Oct. 7, 2013 and Aug. 25, 2014,respectively, in the Japanese Patent Office, the disclosure of which isincorporated herein in their entirety by reference.

TECHNICAL FIELD

The present disclosure relates to a method and apparatus of forming asilicon nitride film.

BACKGROUND

In a semiconductor integrated circuit device, a silicon nitride film hasbeen widely used as a material of an etching stopper, a side wallspacer, a stress liner or the like, as well as as an insulating materialof a gate insulating film. In the related art, there are known methodsof forming such a silicon nitride film.

There is a first conventional method of forming a silicon nitride film(SiBN film) containing boron (B) as a ternary thin film. In the firstconventional method, dichlorosilane (DCS: SiH₂Cl₂) is used as a siliconsource gas and boron trichloride (BCl₃) is used as a boron source gas.Also, the first conventional method includes:

(1) simultaneously supplying the DCS gas and the BCl₃ gas into aprocessing chamber to form a boron-containing silicon film;

(2) purging the interior of the processing chamber;

(3) supplying ammonia (NH₃) as a nitriding gas into the processingchamber such that the boron-containing silicon film is nitrided to bechanged to plasma, thereby forming the SiBN film; and

(4) purging the interior of the processing chamber.

By repeating the processes of (1) to (4), the SiBN film is formed on asurface to be processed of a target object.

The SiBN film formed as above provides the following effects:

a) Better step coverage than that formed using a plasma enhancedchemical vapor deposition (PECVD);

b) A reactive ion etching (RIE)-based etching, that is easier than atypical silicon nitride film (SiN_(x) film) or a typical boron nitridefilm (BN film);

-   -   Better wet etching resistance than the typical boron nitride        film (BN film); and    -   Lower relative dielectric constant than the typical SiN_(x)        film.

Further, there is a second conventional method for forming aboron-containing silicon nitride film (SiBN). In the second method, likethe first conventional method, DCS is used as a silicon source gas andBCl₃ is used as a boron source gas. The second conventional methodincludes:

(1) supplying the DCS gas into a processing chamber to form a siliconfilm;

(2) purging the interior of the processing chamber;

(3) supplying NH₃ as a nitriding gas into the processing chamber suchthat the silicon film is nitrided or is changed to plasma, therebyforming the silicon nitride film;

(4) purging the interior of the processing chamber;

(5) supplying BCl₃ as the boron source gas into the processing chamberto add boron to the silicon nitride film, thereby forming the SiBN film;

(6) purging the interior of the processing chamber;

(7) supplying NH₃ as a nitriding gas into the processing chamber suchthat the boron-containing silicon nitride film is further nitrided byNH₃ activated by plasma and a residual Cl component derived from theBCl₃ gas is removed from an SiBN film; and

(8) purging the interior of the processing chamber.

By repeating the processes of (1) to (8), the SiBN film is formed on asurface to be processed of a target object.

The SiBN film formed as above provides the following effects:

-   -   Better etching resistance by the NH₃ activated by plasma,        compared with a case where the silicon nitride film is not        further plasma-nitirided; and    -   Lower relative dielectric constant than a typical SiN_(x) film.

In the second method, diborane (B₂H₆) and trimethylboron (B(CH₃)₃)containing no halogen element, may be used as the boron source gas, inaddition to the BCl₃ gas.

Also, there is a third conventional method of forming a boron-containingsilicon film (SiBN). In the third conventional method, monosilane (SiH₄)is used as the silicon source gas and BCl₃ is used as the boron sourcegas. In the third conventional method includes:

(1) supplying an SiH₄ gas into a processing chamber to form a siliconfilm;

(2) purging the interior of the processing chamber;

(3) supplying the BCl₃ gas into the processing chamber such that boronis adsorbed onto a surface of the silicon film, thereby forming theboron-containing silicon film; and

(4) purging the interior of the processing chamber.

By repeating the processes of (1) to (4), the boron-containing siliconfilm is formed on a surface to be processed of a target object.

The boron-containing silicon film formed as above provides the followingeffects:

-   -   The silicon film can be formed at lower temperature (e.g., about        350 degrees C.) due to the boron atom acting as a catalyst,        compared with the formation of a silicon film using the SiH₄ gas        alone; and    -   It is obtained good step coverage even at the lower temperature.

Also, in the third conventional method, a B₂H₆ gas containing no halogenelement may be used as the boron source gas, in addition to the BCl₃gas.

Recently, user's demand for a film forming apparatus has beenimpressively changed. Such a demand includes “enhancement ofproductivity of the film forming apparatus.” The enhancement ofproductivity defines maintaining and enhancing the better step coverage,achieving the electrical and physical characteristics required for thinfilms, and obtaining both the better processability and the betteretching resistance, which are imposed on the first and secondconventional methods.

So far, the enhancement of productivity has mainly been focused onimproving so-called hardware, such as an increase in speed of a transferrobot, an increase in control speed of a temperature in a heating deviceor a cooling device, and the like. Unfortunately, in recent years, thehardware improvement alone makes it difficult to meet the user's demandfor productivity.

SUMMARY

Some embodiments of the present disclosure provide a silicon nitridefilm forming method capable of enhancing productivity of a film formingapparatus, while satisfying user's demands such as film uniformity,electrical or physical characteristics and processability, withoutrelying only on hardware improvement, and a film forming apparatusconfigured to perform the film forming method.

According to one embodiment of the present disclosure, provided is amethod of forming a silicon nitride film on a surface to be processed ofa target object, which includes: repeating a first process a firstpredetermined number of times, the process including supplying a siliconsource gas containing silicon toward the surface to be processed andsupplying a decomposition accelerating gas containing a material foraccelerating decomposition of the silicon source gas toward the surfaceto be processed; performing a second process of supplying a nitridinggas containing nitrogen toward the surface to be processed a secondpredetermine number of times; and performing one cycle a thirdpredetermined number of times, the one cycle being a sequence includingthe repetition of the first process and the performance of the secondprocess to form the silicon nitride film on the surface to be processed.

According to another embodiment of the present disclosure, provided is amethod of forming a silicon nitride film on a surface to be processed ofa target object, which includes: supplying a decomposition acceleratinggas toward the surface to be processed, and supplying a silicon sourcegas containing silicon toward the surface to be processed, thedecomposition accelerating gas containing a material for acceleratingdecomposition of the silicon source gas; supplying a nitriding gascontaining nitrogen toward the surface to be processed; and performingone cycle a predetermined number of times, the one cycle being asequence including the supply of the decomposition accelerating gas andthe silicon source gas and the supply of the nitriding gas to form thesilicon nitride film on the surface to be processed.

According to another embodiment of the present disclosure, provided isan apparatus of forming a silicon nitride film on a surface to beprocessed of a target object, which includes: a processing chamberconfigured to perform a film forming process on the target object; asilicon source gas supply mechanism configured to supply a siliconsource gas into the processing chamber; a decomposition accelerating gassupply mechanism configured to supply a decomposition accelerating gasinto the processing chamber; a nitriding gas supply mechanism configuredto supply a nitriding gas into the processing chamber; and a heatingunit configured to heat the processing chamber; and a control unitconfigured to control the silicon source gas supply mechanism, thedecomposition accelerating gas supply mechanism, the nitriding gassupply mechanism, and the heating unit such that the silicon nitridefilm forming method of Claim 1 is performed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the presentdisclosure, and together with the general description given above andthe detailed description of the embodiments given below, serve toexplain the principles of the present disclosure.

FIG. 1 is a flowchart showing an example of a silicon nitride filmforming method according to a first embodiment of the presentdisclosure.

FIGS. 2A to 2N are cross-sectional views showing major processes of theexample of the silicon nitride film forming method according to thefirst embodiment of the present disclosure.

FIG. 3 is a time chart showing a sequence of the silicon nitride filmforming method.

FIG. 4 is a view showing an example of a relationship between atemperature and a growth rate of silicon.

FIG. 5A is a cross-sectional view showing a step coverage according to acomparative example.

FIG. 5B is a cross-sectional view showing a step coverage according tothe first embodiment.

FIG. 6A is a cross-sectional view showing an example where nitrogenelements penetrate in the comparative example.

FIG. 6B is a cross-sectional view showing an example where nitrogenelements penetrate according to the first embodiment.

FIG. 7 is a flowchart showing an example of a silicon nitride filmforming method according to a second embodiment of the presentdisclosure.

FIG. 8 is a vertical cross-sectional view schematically showing a filmforming apparatus according to a third embodiment of the presentdisclosure, which is capable of performing the silicon nitride filmforming methods according to the first and second embodiments.

FIG. 9 is a horizontal cross-sectional view of the film formingapparatus of FIG. 8.

FIG. 10 is a horizontal cross-sectional view schematically showing afilm forming apparatus according to a fourth embodiment of the presentdisclosure, which is capable of performing the silicon nitride filmforming methods according to the first and second embodiments.

FIG. 11 is a flowchart showing a sequence when the silicon nitride filmforming method is performed using the film forming apparatus accordingto the fourth embodiment.

FIG. 12 is a view showing a relationship between the number of cycle anda thickness of a silicon nitride film at every processing temperature.

FIG. 13 is a view showing a relationship between a processingtemperature and a refractive index of a silicon nitride film.

FIG. 14A is a view showing a processing stage in a film formingapparatus 200 a according to a first modified example.

FIG. 14B is a view showing a processing stage in a film formingapparatus 200 b according to a second modified example.

FIG. 14C is a view showing a processing stage in a film formingapparatus 200 c according to a third modified example.

DETAILED DESCRIPTION

In order to enhance productivity of a film forming apparatus, theinventors of the present disclosure focused on improving a film formingsequence of a silicon nitride film, i.e., a software improvement. Also,the inventors of the present disclosure overcame the limits in whichforming a silicon nitride film by using an alternate supply method suchas an atomic layer deposition (ALD) method requires repeating one cycleincluding “supplying a silicon source gas one time and supplying anitriding gas one time” more than once. As a result, a silicon nitridefilm forming method which is capable of enhancing productivity of thefilm forming apparatus, while satisfying user's demands for filmuniformity, electrical characteristics, processability and the like,without relying on hardware improvement, was realized.

Hereinafter, embodiments of the present disclosure will be describedwith reference to the drawings. Further, in the drawings, like referencenumerals indicate like elements. In the following detailed description,numerous specific details are set forth in order to provide a thoroughunderstanding of the present disclosure. However, it will be apparent toone of ordinary skill in the art that the present disclosure may bepracticed without these specific details. In other instances, well-knownmethods, procedures, systems, and components have not been described indetail so as not to unnecessarily obscure aspects of the variousembodiments.

First Embodiment Film Forming Method

FIG. 1 is a flowchart showing a silicon nitride film forming methodaccording to a first embodiment of the present disclosure. FIGS. 2A to2N are cross-sectional views showing major processes of the film formingmethod.

In the first embodiment, a silicon substrate (silicon wafer=siliconsingle crystal) 1 is used as an example of an underlying film on which asilicon nitride film is formed (see FIG. 2A). The underlying film is notlimited to the silicon substrate 1, but may be an insulating film suchas a silicon oxide film, or a conductive film such as a metal film. Inthe first embodiment, the silicon nitride film (which will be describedlater) is formed on a surface to be processed of the silicon substrate1.

Subsequently, the silicon substrate 1 is carried into a processingchamber of the film forming apparatus (which will be described later)where a “silicon film forming process” is performed as a first step. Todo this, a silicon source gas containing silicon is supplied toward thesurface to be processed of the silicon substrate 1 received in theprocessing chamber (step S1 of FIG. 1). In the first embodiment, amonosilane (SiH₄) gas is used as the silicon source gas.

An example of processing conditions in step S1 is follows as:

-   -   Flow rate of monosilane: 1000 sccm    -   Processing time: 30 sec    -   Processing temperature: 200 degrees C.    -   Processing pressure: 133 Pa (1 Torr) (wherein, 1 Torr is defined        as 133 Pa)

Such processing conditions thermally decompose the SiH₄ gas so that theSiHf₄ gas is adsorbed onto the surface to be processed of the siliconsubstrate 1, thus forming a first silicon layer 2-1 (see FIG. 2B). Thefirst silicon layer 2-1 has a thin thickness of tens of atomic layers,for example.

The silicon source gas is not limited to the SiH₄ gas, but any siliconcompound gas may be used as long as it contains silicon. As an example,a so-called high-order silane gas having two or more number of silicon,such as a Si₂H₆ gas, a Si₃H₈ gas or the like, may be used as asilane-based gas. In this embodiment, the silane-based gas is defined asboth a monosilane gas having one silicon and a high-order silane gashaving two or more silicon.

In some embodiments, examples of the silicon source gas may include asilicon compound gas in which a hydrogen atom of the silane-based gas issubstituted with an atom other than the hydrogen atom. As an example,the silicon source gas may be the following gases with the hydrogen atomof the silane-based gas substituted by a chlorine atom:

SiH₃Cl gas,

SiH₂Cl₂ gas,

SiHCl₃ gas,

Si₂H₅Cl gas,

Si₂H₄Cl₂ gas,

Si₂H₃Cl₃ gas,

Si₂H₂Cl₄ gas,

Si₂HCl₅ gas, or the like.

Thereafter, the processing chamber is exhausted, and simultaneously, aninert gas is supplied into the processing chamber to purge the interiorof the processing chamber (step S2 of FIG. 1). Examples of the inert gasmay include a nitrogen (N₂) gas or a rare gas such as an argon (Ar) gas.

Subsequently, a decomposition accelerating gas which contains a materialfor accelerating decomposition of the silicon source gas is suppliedtoward the surface to be processed of the silicon substrate 1 receivedin the processing chamber (step S3 of FIG. 1). An example of thematerial for accelerating the decomposition of the silicon source gasmay be boron (B). In the first embodiment, a diborane (B₂H₆) gas is usedas the decomposition accelerating gas.

An example of processing conditions in step S3 is as follows:

-   -   Flow rate of diborane: 200 sccm    -   Processing time: 30 sec    -   Processing temperature: 200 degrees C.    -   Processing pressure: 133 Pa (1 Torr)

Thus, boron atoms 3 are adsorbed onto the first silicon layer 2-1 (seeFIG. 2C). The boron atoms 3 adsorbed onto the first silicon layer 2-1functions as a catalyst to accelerate the decomposition of the siliconcompound gas (the SiH₄ gas in the first embodiment). With thisconfiguration, even at a low temperature of 100 to 400 degrees C., forexample, the SiH₄ gas can be decomposed faster than a case where none ofthe boron atoms 3 are adsorbed.

The decomposition accelerating gas is not limited to the B₂H₆ gas, butany boron compound gas may be used as long as it contains boron. As anexample, the decomposition accelerating gas may be a BH₃ (monoborane)gas. Further, a so-called high-order borane gas, in which the number ofboron is two or more, may be used as the decomposition accelerating gas.In this embodiment, the borane-based gas is defined as both a monoboranegas having one boron and a high-order borane gas having two or moreboron.

In some embodiments, a boron compound gas with a hydrogen atom of theborane-based gas substituted by an atom other than hydrogen may be usedas the decomposition accelerating gas. As an example, the followinggases with a boron atom of the borane-based gas substituted by achlorine atom may also be used:

-   -   BCl₃ gas,    -   (B(C₂H₅))₃ gas, or the like.

Subsequently, the processing chamber is exhausted, and simultaneously,an inert gas is supplied into the processing chamber to purge theinterior of the processing chamber (step S4 of FIG. 1). This inert gasmay be identical to that used in step S2.

Thereafter, as shown in step S5 of FIG. 1, it is determined whether thenumber of repetitions of a sequence of step S1 to step S4 has reached apredetermined set value n (where n is 2 or greater). If the result ofthe determination is NO, the sequence of step S1 to step S4 is resumed.If the result of the determination is YES, the process proceeds to stepS6.

In this manner, by repeating the sequence of step S1 to step S4 two ormore times, a first silicon film 4-1 is formed on the surface to beprocessed of the silicon substrate 1. FIG. 2D shows an example in whichthe first silicon film 4-1 including the first silicon layer 2-1, asecond silicon layer 2-2 and a third silicon layer 2-3 is formed byrepeating the sequence of step S1 to step S4 three times under thecondition that the predetermination set value n is set to “3”. Also, inFIG. 2D, the boron atoms 3 to be adsorbed onto the third silicon layer2-3 in step S3 are omitted.

Subsequently, a “silicon film nitriding process” as a second step isperformed within the processing chamber where the “the silicon filmforming process” has been performed. To do this, within the processingchamber, a nitriding gas containing nitrogen is supplied to the surfaceto be processed of the silicon substrate 1 on which the first siliconfilm 4-1 is formed (step S6 of FIG. 1). In the first embodiment, anammonia (NH₃) gas is used as the nitriding gas. Also, in the firstembodiment, energy is applied to the NH₃ gas to produce an activenitrogen containing, for example, a nitrogen radical N*, an ammoniaradical NH*, etc. The active nitrogen is supplied toward the surface tobe processed of the silicon substrate 1. An example of the energyapplied to the NH₃ gas may be a high-frequency electric field. As amethod (or mechanism) for generating the high-frequency electric field,for example, a parallel-flat type RF plasma generation mechanismconfigured to generate the high-frequency electric field between twoelectrode plates disposed to face each other may be used.

An example of processing conditions in step S6 is as follows:

-   -   Flow rate of ammonia: 1000 sccm    -   Processing time: 10 sec    -   Processing temperature: 200 degrees C.    -   Processing pressure: 133 Pa (1 Torr)    -   High-frequency electric field: ON

Thus, for example, the first silicon film 4-1 is radical-nitrided suchthat a first silicon nitride film 5-1 is formed (see FIG. 2E).

The nitriding gas is not limited to the NH₃ gas, but any nitrogencompound gas may be used as long as it contains nitrogen. As an example,hydrazine (N₂H₄), hydrazine derivative, or the like may be used as thenitriding gas. In some embodiments, a nitrogen gas alone may be used asthe nitriding gas.

Further, the high-frequency electric field generating method (ormechanism) is not limited to the parallel-flat type RF plasma generationmechanism. As an example, a silent discharge, a radial rod slot antennaor the like may be used.

Thereafter, the high-frequency electric field is turned off, followed byexhausting the processing chamber, followed by supplying an inert gasinto the processing chamber, thus purging the interior of the processingchamber (step S7 of FIG. 1). This inert gas may be identical to thatused in step S2.

Subsequently, as shown in step S8 of FIG. 1, it is determined whetherthe number of repetitions of a sequence of step S6 and step S7 hasreached a predetermined set value p (where p is 1 or greater). If theresult of the determination is NO, the sequence of step S6 and step S7is resumed. If the result of the determination is YES, the processproceeds to step S9.

In this manner, by repeating the sequence of step S6 and step S7 one ormore times, the first silicon film 4-1 is nitrided so that the firstsilicon nitride film 5-1 is formed on the surface to be processed of thesilicon substrate 1. FIG. 2E shows an example in which the first siliconfilm 4-1 is nitrided by performing the sequence of step S6 and step S7once under the condition that the predetermined set value p is set to“1.”

Further, in the first embodiment, the number of repetitions of thenitriding process has been described to be set to a limited value of oneor more. In some embodiments, when the number of repetitions of thenitriding process is set to be one, step S8 may be omitted in a siliconnitride film forming recipe. That is, the recipe may be prepared suchthat step S9 is performed to follow step S7.

In the first embodiment, the sequence of steps S1 to S8 (or S7) isdefined as one cycle including the silicon film forming process (thesequence of steps S1 to S5) in which the plurality of silicon layers2-1, 2-2 and 2-3 are formed and the silicon film nitriding process (thesequence of steps S6 to S8 (or S7).

Subsequently, as shown in step S9 of FIG. 1, it is determined whetherthe number of repetitions of the one cycle has reached a predeterminedset value m (where m is 1 or greater). If the result of thedetermination is NO, the sequence of steps S1 to S8 (or S7) is resumed.If the result of the determination is YES, the process of the siliconnitride film forming method according to the first embodiment isterminated.

In the first embodiment, the predetermined set value m is set to “3” forexample such that and the one cycle including the silicon film formingprocess (the sequence of steps S1 to S5) in which the plurality ofsilicon layers 2-1, 2-2 and 2-3 are formed and the silicon filmnitriding process (the sequence of steps S6 to S8 (or S7)) is performedthree times.

Thus, first, as shown in FIGS. 2F to 2H, by repeating the sequence ofsteps S1 to S4 three times (the predetermined set value n=3), a secondsilicon film 4-2 including a fourth silicon layer 2-4, a fifth siliconlayer 2-5 and a sixth silicon layer 2-6 is formed on the first siliconnitride film 5-1.

Subsequently, as shown in FIG. 21, by performing the sequence of stepsS6 and S7 once (the predetermined set value p=1), the second siliconfilm 4-2 is radical-nitrided to form a second silicon nitride film 5-2.

Thereafter, as shown in FIGS. 2J to 2L, the sequence of steps S1 to S4is repeatedly performed three times again such that a third silicon film4-3 including a seventh silicon layer 2-7, an eighth silicon layer 2-8and a ninth silicon layer 2-9 is formed on the second silicon nitridefilm 5-2.

Subsequently, as shown in FIG. 2M, by repeating the sequence of steps S6and S7 once, the third silicon film 4-3 is radical-nitrided to form athird silicon nitride film 5-3.

In this manner, as shown in FIG. 2N, a silicon nitride film 5 is formedon the surface to be processed of the silicon substrate 1.

The silicon nitride film forming method according to the firstembodiment can provide the following effects.

(Enhancement of Throughput)

FIG. 3 is a time chart showing sequences of the silicon nitride filmforming method. In FIG. 3, the silicon nitride film forming methodaccording to the first embodiment and a silicon nitride film formingmethod according to a comparative example are shown to be compared on atime axis. In the film forming method according to the comparativeexample, one cycle is set to include supplying a silicon source gas, adecomposition accelerating gas and a nitriding gas one time,respectively. The one cycle is repeated a plurality of times. Also, itis assumed that a supply time of the silicon source gas, a supply timeof the decomposition accelerating gas, a supply time of the nitridinggas and a purge time are the same in both the first embodiment and thecomparative example.

As shown in FIG. 3, in the silicon nitride film forming method accordingto the first embodiment, the one cycle is set to include “supplying thesilicon source gas and the decomposition accelerating gas a plurality oftimes, respectively” and “supplying the nitriding gas one time”. Withthis configuration, compared with the comparative example in which onecycle includes “supplying the silicon source gas, the decompositionaccelerating gas and the nitriding gas one time, respectively,” thenumber of the supply of the nitriding gas can be reduced. For example,in the first embodiment, each of the silicon source gas and thedecomposition accelerating gas is supplied three times while thenitriding gas is supplied one time, which makes it possible to reducethe supply of the nitriding gas and the purging process twice,respectively. This shortens a processing time. Further, the shortenedprocessing time is accumulated each time the one cycle is repeated.Thus, assuming that the silicon nitride film is formed by supplying thesilicon source gas and the decomposition accelerating gas 60 times, thefollowing results is obtained:

-   -   Comparative example: supplying the nitriding gas 60 times    -   First embodiment: supplying the nitriding gas 20 times

Thus, according to the first embodiment, the number of the supply of thenitride gas and the purging process can be reduced as many as 40 timesless than that of the comparative example, which makes it possible toshorten the processing time as much.

Also, assuming that the silicon nitride film is formed by supplying thesilicon source gas 120 times, the following results is obtained:

-   -   Comparative example: supplying the nitriding gas 120 times    -   First embodiment: supply the nitriding gas 40 times

In this case, according to the first embodiment, the number of thesupply of the nitriding gas and the purging process can be reduced asmany as 80 times less than that of the comparative example.

As described above, the shortening of the processing time according tothe first embodiment increases as the number of the supply of thesilicon source gas increases.

(Good Step Coverage)

In the comparative example, shortening the processing time requiresincreasing an amount of a silicon film to be formed by a single supplyof the silicon source gas and decreasing the number of cycle required toform a desired thickness of the silicon film based on a design value. Tothis end, it is necessary to increase a film formation temperature up toa temperature at which silicon initiates to a chemical mechanicaldeposition (CVD) growth, thereby increasing a growth rate. As for thegrowth rate and the film formation temperature, the growth rate tends toincrease as the film formation temperature increases. FIG. 4 shows anexample of a relationship between a film formation temperature and agrowth rate of silicon.

Microscopically analyzing that the tendency for the growth rate toincrease as the film formation temperature increases, as shown in FIG.4, a slight “fluctuation” appears in the growth rate at a range oftemperature of less than 400 degrees C. Specifically, as shown in FIG.4, the growth rate of the silicon starts to increase to about 100degrees C. and continues to gradually increase to about 300 degrees C.When the film formation temperature exceeds 300 degrees C., the growthrate starts to go up. When the film formation temperature exceeds 400degrees C., the growth rate rapidly increases.

Such a “fluctuation” is estimated to occur as a function of whether thesilicon is adsorbed onto or deposited on an underlying film. Forexample, at a temperature of 100 degrees C. to 300 degrees C., it isconsidered that the silicon is only adsorbed onto the underlying film orthe adsorption of the silicon becomes dominant. Further, it isconsidered that, in a temperature of 300 degrees C. or higher, siliconis further deposited on the adsorbed silicon, that is, the siliconinitiates to the CVD growth, although being a few. Also, at atemperature of 400 degrees C. or higher, deposition of the siliconbecomes dominant so that the silicon initiates to an almost complete CVDgrowth.

Thus, in order to increase a film forming rate of the silicon when thesilicon source gas is supplied one time, the film formation temperatureis required to be maintained at 400 degrees C. or higher. However, oncethe silicon initiates to the CVD growth, as shown in FIG. 5A, forexample, coatability (or step coverage) of convex portions 10 or concaveportions 11 in the first silicon film 4-1, which are formed on thesurface to be processed of the substrate 1, may be degraded.

According to the first embodiment, the film formation temperature of thesilicon is not necessarily increased to a temperature at which the CVDgrowth initiates in order to shorten the processing time.

Therefore, as shown in FIG. 5B, the first silicon film 4-1 can be formedwhile maintaining the good step coverage. Such an advantage may still beobtained for the second silicon film 4-2 or a silicon film to be formedone the second silicon film 4-2. As a result, the thick silicon nitridefilm 5, which is formed by sequentially nitriding the silicon films 4-1,4-2, . . . , each having good step coverage, has also good stepcoverage.

(Suppressing Penetration of Nitrogen)

In the comparative example, the first silicon film 4-1 formed when thefilm formation temperature of the silicon is not increased up to the CVDgrowth initiation temperature has a very thin thickness. As such, uponnitriding the first silicon film 4-1, as shown in FIG. 6A, nitrogenatoms N may penetrate through the first silicon film 4-1 to reach theunderlying film. Upon penetrating the nitrogen atoms N, in a case wherethe underlying film is the silicon substrate 1, a region near thesurface to be processed of the silicon substrate 1 may be modified intoa silicon nitride 12. In addition, in a case where the underlying filmis silicon oxide, the region near the surface to be processed may bemodified into silicon oxynitride. That is, the comparative example has ahigh likelihood that the underlying film is modified into anothermaterial.

Under these circumstances, according to the first embodiment, the firstsilicon film 4-1 is obtained by stacking the plurality of silicon layers2-1 to 2-3. This allows the first silicon film 4-1 to have a sufficientthickness enough to suppress the penetration of the nitrogen atoms N.Further, as shown in FIG. 6B, in the case where the first silicon film4-1 has the sufficient thickness enough to suppress the penetration ofthe nitrogen atoms N, when performing the nitriding process, it ispossible to suppress the nitrogen atoms N contained in the first siliconfilm 4-1 from reaching the underlying film, (e.g., the silicon substrate1), which makes it possible to reduce the modification of the underlyingfilm into another material.

(Improved Controllability for Concentration of Nitrogen Contained inSilicon Nitride Film)

A stoichiometric composition ratio of a silicon nitride film is“Si:N=3:4 (Si₃N₄).” However, the silicon nitride film may have variouscomposition ratios depending on a film forming method. Also, aconcentration of nitrogen contained in the silicon nitride film, thatis, the composition of the silicon nitride film influences, for example,a film stress. As an example, for a Si-rich composition (in the Si₃N₄composition), the film stress is small, while for the N-rich composition(in the Si₃N₄ composition), the film stress increases.

With regards to the silicon nitride film forming method according to thefirst embodiment, the concentration of the nitrogen can be controlled bychanging a supply time and a flow rate of the nitriding gas in thesilicon film nitriding process (the sequence of steps S6 and S7), andthe number of the sequence of steps S6 and S7. In some embodiments, theconcentration of the nitrogen can be controlled by changing the numberof repetitions of the silicon film forming process (the sequence ofsteps S1 to S4).

As an example, when one cycle includes “supplying the silicon source gasonce” and “supplying the nitriding gas once” as in the comparativeexample, the number of the supply of the nitriding gas tends to increaseuntil the thickness of the silicon nitride film reaches a design value.This makes it difficult to suppress the concentration of the nitrogen toa low level.

Under these circumstances, according to the first embodiment, the numberof repetitions of the silicon film forming process (the sequence ofsteps S1 to S4) is increased to increase the thickness of the siliconfilm 4 (4-1, 4-2, . . . ,), thus increasing a content (or ratio) ofsilicon contained in the silicon nitride film 5. This allows a ratio ofthe nitrogen contained in the silicon nitride film 5 to be relativelysuppressed. As a result, a selectable concentration range of thenitrogen can be expanded compared with the comparative example.

As described above, according to the first embodiment, it is possible toimprove the control of the amount of concentration of the nitrogencontained in the silicon nitride film.

<For a Range of Film Formation Temperature>

Hereinafter, a range of film formation temperature will be described.

As described above with reference to FIG. 4, when forming the siliconfilm, a slight “fluctuation” occurs in the growth rate at a range oftemperature of less than 400 degrees C. The reason for this is that, atthe range of temperature of less than 400 degrees C., there are a rangeof temperature at which only adsorption occurs (or adsorption becomesdominant) and a range of temperature at which both adsorption anddeposition occur (or a range of temperature at which the adsorption istransited to the CVD growth). At a temperature of 400 degrees C. orabove, deposition starts to take place, that is, the silicon film beginsan almost substantial CVD growth (the silicon can be deposited even withthe SiH₄ gas alone).

As described above, when the silicon film begins the CVD-growth, a filmformation rate is remarkably increased, while a step coverage may bedegraded. Based on this, in the silicon nitride film forming methodaccording to the first embodiment, the silicon film 4 (4-1, 4-2, . . . )may be formed at a temperature less than a temperature at which thealmost complete CVD growth starts to take place.

That is, in some embodiments, the film formation temperature of thesilicon film 4 (4-1, 4-2, . . . ,) in step S1 may be set to a range offrom a temperature at which the silicon initiates to be adsorbed ontothe surface to be processed to less than a temperature at which thesilicon initiates the CVD growth. An example of the temperature rangemay be a range of from 100 degrees C. to less than 400 degrees C. (inthis range, adsorption or deposition of the silicon initiates with theB₂H₆ gas that reacts with the adsorbed SiH₄ gas).

In some embodiments, an example of the temperature range may be a rangeof more than the adsorption initiation temperature at which the siliconinitiates to be adsorbed onto the surface to be processed to less thanthe CVD growth transition initiation temperature. At a range oftemperature of from the CVD growth transition initiation temperature toless than the CVD growth initiation temperature, it is considered thatboth the adsorption and the slight CVD growth of the silicon coexist.The slight CVD growth of the silicon may cause that the surface of thesilicon film 4 (4-1, 4-2, . . . ) has fine unevenness. To address this,in some embodiments, the film formation temperature of the silicon film4 (4-1, 4-2, . . . ) in step S1 may be set to fall within a temperaturerange of from the adsorption initiation temperature to less than the CVDgrowth transition initiation temperature. Thus, the silicon film 4 (4-1,4-2, . . . ) may be formed by the adsorption substantially. Examples ofthe temperature range may include a range of from 100 degrees C. to lessthan 300 degrees C.

<For Decomposition Accelerating Gas>

Next, the decomposition accelerating gas will be described.

As described above, lowering of the film formation temperature of thesilicon film 4 (4-1, 4-2, . . . ) in step S1 to less than the CVD growthinitiation temperature requires supplying the decomposition acceleratinggas including a material for accelerating decomposition of the siliconsource gas, as shown in step S3. Upon supplying the decompositionaccelerating gas, the adsorbed SiH₄ and the decomposition acceleratinggas (e.g., B₂H₆) react with each other so that the silicon is adsorbedor deposited. Accordingly, compared to the case where no decompositionaccelerating gas is supplied, it is possible to generate thedecomposition (e.g., thermal decomposition) of the silicon source gas ata relatively low temperature, thus adsorbing or depositing the siliconat a low temperature.

The effect of the thermal decomposition at the low temperature maydiffer depending on a material used in accelerating the thermaldecomposition. In some embodiments, examples of the material may be theaforementioned boron. Therefore, a boron compound gas containing boronmay be used as the decomposition accelerating gas.

Further, the effect of the thermal decomposition at the low temperaturemay differ depending on the boron compound gas. In the first embodiment,a boron-hydrogen-based compound gas (borane-based gas) and aboron-halogen-based compound gas (BCl₃ gas) are used as the boroncompound gas.

In comparison with the borane-based gas and the boron-halogen-based gas,the borane-based gas has a greater effect in the thermal decompositionat the low temperature. For example, the use of the B₂H₆ gas as theborane-based gases enables the film formation temperature of the siliconfilm 4 (4-1, 4-2, . . . ) in step S1 to be lowered to 200 degrees C. orless. At a point of view of lowering the film forming temperature, theborane-based gas may be selected as the decomposition accelerating gas.

Further, it is considered that, in the related art, both the siliconsource gas and the boron source gas are supplied into the processingchamber, but the related art does not describe any catalytic action byboron, or whether the catalytic action is weaker than that described inthe first embodiment, if any. This is because that, upon simultaneouslysupplying the silicon source gas and the boron source gas into theprocessing chamber, the boron is difficult to adsorb onto the surface tobe processed in a high density.

Also, it is considered that, in the related art, the boron source gas issupplied into the processing chamber. Similarly, the related art doesnot disclose the catalytic action by boron, or whether the catalyticaction is weaker than that described in the first embodiment, if any.This is because the boron-containing silicon nitride film is furtherplasma-nitrided, thereby reducing a density of the boron to be formedonto the surface to be processed.

Based on these circumstances, it may be desirable that the decompositionaccelerating gas is supplied before the supply of the silicon source gasor before the nitridation of the silicon film. Based on this, forexample, step S1 and step S3 shown in FIG. 1 may be interchanged.Specifically, after the decomposition accelerating gas is supplied (stepS3), the purging process is performed, followed by supplying the siliconsource gas (step S1). Subsequently, the subsequent purging process isperformed. In this way, step S1 and S3 may be interchanged.

<Silicon Film Nitriding Process>

Hereinafter, the silicon film nitriding process will be described.

In the first embodiment, when the silicon film 4 (4-1, 4-2, . . . ) isnitrided, the energy other than heat has been described to be applied tothe nitriding gas. With this configuration, it is possible to nitridethe silicon film 4 (4-1, 4-2, . . . ) at the low temperature, forexample, at a temperature (e.g., 200 degrees C.) identical to the filmformation temperature of the silicon film 4 (4-1, 4-2, . . . ).Specifically, in the first embodiment, active nitrogen (e.g., at leastnitrogen radicals) is produced within the processing chamber by furtherapplying the electrical energy (e.g., high-frequency power) to thenitriding gas. And then, the generated nitrogen radicals are allowed toreact with the silicon film 4 (4-1, 4-2, . . . ) within the processingchamber to thereby nitride the silicon film 4 (4-1, 4-2, . . . ).

In this case, if the silicon source gas or the decompositionaccelerating gas used in the above contains a halogen element, a smallamount of the halogen element may remain in the silicon film 4 (4-1,4-2, . . . ). In the first embodiment, chlorine atoms may remain. Eventhough the chlorine atoms remain in the silicon film 4 (4-1, 4-2, . . .), it does not make any difference if the amount of chlorine atomsremained in the silicon film 4 is a little. However, in consideration ofreducing the size of the silicon film 4 in the future, the small amountof chlorine atoms may have high possibility of affecting a filmformation sequence of the silicon nitride film 5.

In particular, in the first embodiment, when the silicon film 4 (4-1,4-2, . . . ) is nitrided, the electrical energy is further applied. Whenthe electrical energy is applied to the small amount of chlorine atomsremaining in the silicon film 4 (4-1, 4-2, . . . ), the chlorine atomsmay be separated from the silicon atoms or boron atoms, thereby causinga chlorine radical, a chlorine plasma, a chlorine ion, or the likewithin the processing chamber.

The chlorine radical, the chlorine plasma and the chlorine ion areetchants used for plasma etching the silicon. That is, when the siliconfilm 4 (4-1, 4-2, . . . ) is nitrided, a material used as the etchant islikely to be produced from the silicon film 4 (4-1, 4-2, . . . ). Whenthe etchant that etches the silicon is produced within a reactionchamber, an etching reaction of taking the silicon atoms from thesilicon film 4 (4-1, 4-2, . . . ) may simultaneously occur. An exampleof a reaction formula when the etchant is chlorine is as follows:

Si+4Cl→SiCl₄↑

When the etching action as described above occurs simultaneously whenthe silicon film 4 (4-1, 4-2, . . . ) is nitrided, a thickness of thesilicon film 4 (4-1, 4-2, . . . ) may be reduced or the surfaceroughness of the silicon film 4 (4-1, 4-2, . . . ) may be degraded. Thismay easily occur, especially when the energy other than heat is furtherapplied when the silicon film 4 (4-1, 4-2, . . . ) is nitrided.

Thus, in the case in which the energy other than heat is further appliedwhen the silicon film 4 (4-1, 4-2, . . . ) is nitrided, suppressing theetching action of the silicon film 4 (4-1, 4-2, . . . ) may require thefollowing plan:

(a) Using a silicon compound gas containing no halogen elements as thesilicon source gas, and

(b) Using a compound gas containing no halogen elements as thedecomposition accelerating gas.

At least one of the plans (a) and (b) may be employed. In someembodiments, both the plans (a) and (B) may be employed.

This plan suppresses the etching action from being occurred, when thesilicon film 4 (4-1, 4-2, . . . ) is nitrided, which can control thefilm thickness better and prevent degradation in the surface roughness.

In some embodiments, the following plans may be employed:

(c) Using a silane-based gas as the silicon source gas, and

(d) Using a borane-based gas used as the decomposition accelerating gas.

Employing both the plans (c) and (d) may realize both the plans (a) and(b). In addition, the silicon film may be implemented by only threeelements of silicon, hydrogen and boron, in fact.

Hydrogen is an element playing a key role in forming an amorphoussilicon film. Also, when boron is contained at a rate of less than 1% ina silicon nitride film to be formed, the formed silicon nitride film, infact, may be handled as a silicon nitride film (SiN). Conversely, whenthe boron is contained in the formed silicon nitride film at a rate ofmore than 1%, the formed silicon nitride film may be handled as aboron-containing silicon nitride film (SiBN). Such a boron is an elementthat does not do any harm even when existing in the silicon nitridefilm, and acts as an essential element in the formation of the SiBNfilm.

As described above, by simultaneously employing both the plans (c) and(d), it is possible to prevent an unnecessary element from remaining orbeing mixed in the formed silicon nitride film, thus forming a siliconnitride film of a better quality.

<Method of Selectively Producing SiN Film and SiBN Film>

Next, a method of selectively produced an SiN film and an SiBN film willbe described.

The use of the boron compound gas as the decomposition accelerating gasenables the boron to be contained in the formed silicon nitride film 5.The silicon nitride film 5 may be produced as any one of the SiN filmand the SiBN film by controlling the content of boron.

In a specific example, when the content of boron contained in the formedsilicon nitride film 5 is less than 1%, the formed silicon nitride film5, in fact, may be handled as the silicon nitride film (SiN).

Also, when the content of boron contained in the formed silicon nitridefilm 5 is equal to or greater than 1%, the formed silicon nitride film 5may be regarded as the boron-containing silicon nitride film (SiBN).

In this manner, the SiN film and the SiBN film can be selectivelyproduced by using the boron compound gas as the decompositionaccelerating gas and controlling the content of boron in the formedsilicon nitride film 5, which makes it possible to realize a highutilization of the film forming process.

<Film Formation Temperature and Nitridation Temperature of Silicon Film>

Hereinafter, a film formation temperature and a nitridation temperatureof the silicon film 4 (4-1, 4-2, . . . ) will be described.

By using the decomposition accelerating gas in the formation of thesilicon film 4 (4-1, 4-2, . . . ) and also applying the energy otherthan heat to the nitriding gas in the nitridation of the silicon film 4(4-1, 4-2, . . . ), it is possible to lower both the film formationtemperature and the nitridation temperature to a low temperature of,e.g., less than 400 degrees C.

This configuration enables the film formation temperature and thenitridation temperature of the silicon film 4 (4-1, 4-2, . . . ) to beequal to each other. Thus, there is no need for changing an internaltemperature of the processing chamber in the transition of the formingprocess of the silicon film (step S1 to step S4) to the nitridingprocess of the silicon film (step S6 and step S7).

The change of the internal temperature of the processing chamber causesa waiting time such as a period of heating-up time and a period ofheating-down time during which the film forming process for a targetobject pauses.

Such a waiting time may be reduced by making the film formationtemperature and the nitridation temperature of the silicon film 4 (4-1,4-2, . . . ) to be identical. The reduction of the waiting time furtherenhances productivity of the silicon nitride film forming methodaccording to the first embodiment.

Second Embodiment

In the silicon nitride film forming method according to the firstembodiment, step S1 and step S3 have been described to be interchanged.The second embodiment is a specific example in which step S1 and step S3are interchanged.

FIG. 7 is a flowchart showing an example of a silicon nitride filmforming method according to the second embodiment of the presentdisclosure.

As shown in FIG. 7, in the second embodiment, the silicon substrate 1 iscarried into the processing chamber of the film forming apparatus, andsubsequently, the decomposition accelerating gas as described above issupplied toward the surface to be processed of the silicon substrate 1inside the processing chamber (step S3). The processing conditions instep S3 may be identical to those in step S3 described in the firstembodiment.

Subsequently, for example, an inert gas is supplied into the processingchamber while exhausting the processing chamber such that the interiorof the processing chamber is purged (step S2). The inert gas used instep S2 may be similar to that described in the first embodiment.

Thereafter, the silicon source gas containing silicon is supplied towardthe surface to be processed of the silicon substrate 1 (step S1). Theprocessing conditions in step S4 may be similar to those of step S1described in the first embodiment.

Subsequently, for example, an inert gas is supplied into the processingchamber while exhausting the processing chamber such that the interiorof the processing chamber is purged (step S4). The inert gas used instep 4 may be similar to that described in the first embodiment.

Subsequently, as shown in step S5 of FIG. 7, it is determined whetherthe number of repetitions of the sequence of steps S3-S2-S1-S4 which isdefined as the silicon film forming process has reached thepredetermined set value n (where n is 1 or greater). If the result ofthe determination is NO, the sequence of steps S3-S2-S1-S4 is resumed.If the result of the determination is YES, the process proceeds to stepS6 as in the first embodiment. Subsequently, the sequence of steps S6and S7 as the silicon film nitriding process is performed p number oftimes as the predetermined set value (where p is 1 or greater).Thereafter, as shown in step S9, it is determined that the number of asequence in which the silicon film forming process and the silicon filmnitriding process are defined as one cycle has reached the predeterminedset value m (where m is 1 or greater). If the result of thedetermination is NO, the sequence is resumed. If the result of thedetermination is YES, the process of the silicon nitride film formingmethod according to the second embodiment is terminated.

As described above, the supply of the silicon source gas (step S1) andthe supply of the decomposition accelerating gas (step S3) may beinterchanged such that the decomposition accelerating gas is firstsupplied (step S3), followed by supplying the silicon source gas (stepS1).

In the first embodiment, the predetermined set value n in step S5 is setto be 2 or greater, while in the second embodiment, the decompositionaccelerating gas is supplied to the surface to be processed of thesilicon substrate 1 prior to the supply of the silicon source gas sothat the predetermined set value n in step S5 is set to be 1 or greater.This improves throughput and reduces the use of the silicon source gasand the decomposition accelerating gas. Further, according to thesilicon nitride film forming method according to the second embodiment,it is possible to increase a degree of freedom of the film formingprocess.

<Film Forming Apparatus>

Hereinafter, a film forming apparatus according to a third embodimentsof the present disclosure, which is capable of implementing the siliconnitride film forming method according to the first and secondembodiments of the present disclosure, will be described.

FIG. 8 is a vertical cross-sectional view schematically showing a filmforming apparatus 100 according to a third embodiments of the presentdisclosure, which is capable of implementing the silicon nitride filmforming method according to the first and second embodiments of thepresent disclosure, and FIG. 9 is a horizontal cross-sectional view ofthe film forming apparatus 100 of FIG. 8 when viewed from the top.

As shown in FIGS. 8 and 9, the film forming apparatus 100 includes acylindrical processing chamber 101 having a ceiling with a lower endopened. The entirety of the processing chamber 101 is formed of, e.g.,quartz. A quartz ceiling plate 102 is installed at the ceiling insidethe processing chamber 101. A cylindrical manifold 103 formed of, e.g.,stainless steel, is connected to a lower end opening portion of theprocessing chamber 101 through a sealing member 104 such as an O-ring.

The manifold 103 supports a lower end portion of the processing chamber101. A vertical wafer boat 105 is inserted into the processing chamber101 through a lower portion of the manifold 103. The vertical wafer boat105 includes a plurality of rods 106 having a plurality of supportrecesses (not shown) formed therein. A plurality of (e.g., 50 to 100)semiconductor substrates (in this example, the silicon substrates 1) astarget objects is supported by the support recesses. In this example,portions of respective peripheries of the silicon substrates 1 aresupported by the support recesses. With this configuration, in thevertical wafer boat 105, the silicon substrates 1 are loaded inmultiple-stages. Thus, the plurality of silicon substrates 1 isaccommodated in the processing chamber 101 in a height direction.

The vertical wafer boat 105 is mounted on a table 108 through a quartzheat insulation tube 107. The table 108 is supported on a rotary shaft110 that pierces a cover 109 that is formed of, e.g., a stainless steel,to open/close a bottom opening of the manifold 103. For example, amagnetic fluid seal 111 is installed at a piercing portion of the rotaryshaft 110 to seal the rotary shaft 110 tightly and support the rotaryshaft 110 rotatably. A seal member 112 formed of, for example, an Oring, is installed between a peripheral portion of the cover 109 and abottom end of the manifold 103. Accordingly, the sealing state in theprocessing chamber 101 is maintained. The rotary shaft 110 is installedat a front end of an arm 113 supported by an elevating mechanism (notshown) such as a boat elevator. Thus, the vertical wafer boat 105, thecover 109 and the like are elevated in an integrated manner to beinserted into/separated from the processing chamber 101.

The film forming apparatus 100 includes a process gas supply mechanism114 configured to supply a process gas into the processing chamber 101,and an inert gas supply mechanism 115 configured to supply an inert gasinto the processing chamber 101.

In this example, the process gas supply mechanism 114 includes a siliconsource gas supply source 117 a, a decomposition accelerating gas supplysource 117 b, and a nitriding gas supply source 117 c. The inert gassupply mechanism 115 includes an inert gas supply source 120.

A silicon source gas supplied from the silicon source gas supply source117 a is used in step S1 shown in FIG. 1. An example of silicon sourcegas may be an SiH₄ gas. A decomposition accelerating gas supplied fromthe decomposition accelerating gas supply source 117 b is used in stepS3 shown in FIG. 1. An example of the decomposition accelerating gas maybe a B₂H₆ gas. A nitriding gas supplied from the nitriding gas supplysource 117 c is used in step S6 shown in FIG. 1. An example of thenitriding gas may be an NH₃ gas. An inert gas supplied from the inertgas supply source 120 is used to dilute the gases supplied into theprocessing chamber 101 or perform the purging process in steps S2, S4and S7 shown in FIG. 1. An example of the inert gas may be an Ar gas.

The silicon source gas supply source 117 a is coupled to a dispersionnozzle 123 a through a flow rate controller 121 a and an on-off valve122 a. The decomposition accelerating gas supply source 117 b is coupledto a dispersion nozzle 123 b (not shown in FIG. 8, and see FIG. 9)through a flow rate controller 121 b and an on-off valve 122 b. Thenitriding gas supply source 117 c is coupled to a dispersion nozzle 123c through a flow rate controller 121 c and an on-off valve 122 c.

Each of the dispersion nozzles 123 a to 123 c includes a quartz pipe,pierces a side wall of the manifold 103 inward, bends upward, andextends vertically. At a vertical portion of each of the dispersionnozzles 123 a to 123 c, a plurality of gas discharge holes 124 is formedspaced apart from one another by a predetermined distance. Thus, eachgas is approximately uniformly discharged from the respective gasdischarge holes 124 into the processing chamber 101 in a horizontaldirection.

A plasma generation mechanism 140 is formed in a portion of a side wallof the processing chamber 101. The plasma generation mechanism 140 isused as an energy application mechanism configured to apply energy tothe nitriding gas so as to generate at least active nitrogen. The plasmageneration mechanism 140 includes a plasma partition wall 141 which istightly welded to an outer wall of the processing chamber 101. Theplasma partition wall 141 is formed of, for example, quartz. The plasmapartition wall 141 has a concave cross section shape to cover an opening142 formed in the side wall of the processing chamber 101. The opening142 has an elongated shape formed by chipping the side wall of theprocessing chamber 101 in a vertical direction such that all of thesilicon substrates 1 supported by the vertical wafer boat 105 in thevertical direction are covered. In this example, the dispersion nozzle123 c configured to discharge the nitriding gas is disposed in an innerspace defined by the plasma partition wall 141, i.e., in a plasmageneration space.

The plasma generation mechanism 140 includes a pair of elongated plasmaelectrodes 143 and a high-frequency power source 145 connected to eachof the plasma electrodes 143 through a power feed line 144. The pair ofelongated plasma electrodes 143 is disposed to vertically face eachother on outer surfaces of both side walls of the plasma partition wall141. The high-frequency power source 145 supplies a high-frequency powerto the pair of plasma electrodes 143 through the power feed line 144.The high-frequency power source 145 applies a high-frequency voltage of,e.g., 13.56 MHz, to the pair of plasma electrodes 143. Thus, ahigh-frequency electric field is applied in the plasma generation spacedefined by the plasma partition wall 141. The nitriding gas dischargedfrom the dispersion nozzle 123 c is converted to plasma within theplasma generation space to which the high-frequency electric field isapplied. The converted plasma is supplied into the processing chamber101 as a plasma gas containing, e.g., an active nitrogen such as anitrogen radical (N*) or an ammonia radical (NH*), through the opening142. Further, in the film forming apparatus 100, when supplying thehigh-frequency power to the pair of plasma electrodes 143 is stopped,the nitriding gas discharged from the dispersion nozzle 123 c, withoutbeing converted to plasma, may be supplied into the processing chamber101.

At an outer side of the plasma partition wall 141, an insulationprotection cover 146 made of, e.g., quartz, is installed to cover theplasma partition wall 141. A coolant flow path (not shown) is formed atan inner portion of the insulation protection cover 146 such that theplasma electrodes 143 can be cooled by a cooled nitrogen gas flowingthrough the coolant flow path.

The inert gas supply source 120 is coupled to a nozzle 128 through aflow rate controller 121 d and an on-off valve 122 d. The nozzle 128penetrates through the side wall of the manifold 103 to discharge theinert gas from a front end thereof in the horizontal direction.

At a portion opposite to the dispersion nozzles 123 a to 123 c in theprocessing chamber 101, an exhaust vent 129 is formed to exhaust theprocessing chamber 101. The exhaust vent 129 has an elongated shapeformed by vertically chipping the side wall of the processing chamber101. At a portion corresponding to the exhaust vent 129 of theprocessing chamber 101, an exhaust vent cover member 130 with a C-shapedsection is installed by welding to cover the exhaust vent 129. Theexhaust vent cover member 130 extends upward along the side wall of theprocessing chamber 101, and defines a gas outlet 131 at the top of theprocessing chamber 101. An exhaust mechanism 132 including a vacuumpump, or the like is connected to the gas outlet 131. The exhaustmechanism 132 exhausts the processing chamber 101 to discharge theprocess gas and to change an internal pressure of the processing chamber101 into a process pressure.

A cylindrical body-shaped heating device 133 is installed on the outerperiphery of the processing chamber 101. The heating device 133activates a gas supplied into the processing chamber 101, and heats thetarget object (the silicon substrates 1 in this example) accommodatedwithin the processing chamber 101.

For example, the components of the film forming apparatus 100 arecontrolled by a controller 150 including a microprocessor (e.g., acomputer). The controller 150 is connected to a user interface 151including a keyboard for inputting, by an operator, a command to controlthe film forming apparatus 100, and a display unit for displaying anoperation state of the film forming apparatus 100.

A memory unit 152 is connected to the controller 150. The memory unit152 stores a control program for executing various processes in thefilm-forming apparatus 100 under the control of the controller 150, anda program (i.e., a recipe) for executing a process in each component ofthe film-forming apparatus 100 according to the process conditions. Forexample, the recipe is stored in a memory medium of the memory unit 152.The memory medium may include a hard disk, a semiconductor memory, aCD-ROM, a DVD, and a portable memory such as a flash memory. The recipemay be suitably transmitted from other devices through a dedicated line.If necessary, the recipe is read from the memory unit 152 in response toa command received from the user interface 151, and the controller 150executes a process according to the read recipe. Accordingly, thefilm-forming apparatus 100 performs a desired process under the controlof the controller 150.

The silicon nitride film forming method according to the first andsecond embodiments of the present disclosure is performed using the filmforming apparatus 100 as shown in FIGS. 8 and 9, which includes thecontroller 150 configured to control the silicon source gas supplysource 117 a, the decomposition accelerating gas supply source 117 b,the nitriding gas supply source 117 c, the heating device 133, and theplasma generation mechanism 140.

<Film Forming Apparatus: Second Example>

FIG. 10 is a horizontal cross-sectional view schematically showing asecond example of a film forming apparatus capable of performing thesilicon nitride film forming method according to the first and secondembodiments of the present disclosure.

The film forming apparatus is not limited to the batch-type verticalfilm forming apparatus as shown in FIGS. 8 and 9. In some embodiments, ahorizontal batch-type film forming apparatus 200 as shown in FIG. 10 maybe used as the film forming apparatus. In FIG. 10, a horizontalcross-section of a processing chamber 202 of the horizontal batch-typefilm forming apparatus 200 is schematically shown. Further, in FIG. 10,a process gas supply mechanism, an inert gas supply mechanism, anexhaust device, a heating device, a controller, and the like is omitted.Also, the film forming apparatus 200 of the second example may beeffectively used, especially for the silicon nitride film forming methodaccording to the second embodiment. Thus, the film forming apparatus 200of the second example will be described based on the assumption that itis applied to the silicon nitride film forming method according to thesecond embodiment.

As shown in FIG. 10, the film forming apparatus 200 performs a filmforming process on a plurality of (e.g., 5) silicon substrates 1 whichis mounted on a turntable 201 in a circumferential direction. Theturntable 201 is installed within the processing chamber 202 of the filmforming apparatus 200. The turntable 201 rotates in a counterclockwisedirection, for example.

The interior of the processing chamber 202 is divided into sixprocessing stages PS1 to PS6. Once the turntable 201 rotates, thesilicon substrates 1 go the circuit of the six processing stages. Inthis example, once the turntable 201 rotates once, one cycle includingthe silicon film forming process and the silicon film nitriding processis carried out. Specifically, the five silicon substrates 1 are mountedon the turntable 201, and subsequently, a decomposition accelerating gas(e.g., diborane gas) is first supplied as a catalyst of the acceleratingdecomposition into the processing chamber 202 such that the diborane gasis adsorbed onto each of the silicon substrates 1. Thereafter, a siliconsource gas is supplied into the processing chamber 202 such that asilicon film is formed on each of the silicon substrates 1. And then,plasma is ignited to nitride the silicon films. Under thesecircumstances, the gas is continuously supplied during a predeterminedcycle while rotating the turntable 201.

The first processing stage PS1 corresponds to step S3 shown in FIG. 7.In the processing stage PS1, the decomposition accelerating gas issupplied toward a surface to be processed of each of the siliconsubstrates 1. A gas supply pipe 203 a through which the decompositionaccelerating gas is supplied, is disposed at an upper side of the firstprocessing stage PS 1. The decomposition accelerating gas supplied fromthe gas supply pipe 203 a is applied toward the surfaces to be processedof the respective silicon substrates 1 which are exposed in the firstprocessing stage PS 1 while being mounted on the turntable 201. At aportion corresponding to the first processing stage PS1 in theprocessing chamber 202, an exhaust vent 204 a is formed to discharge thedecomposition accelerating gas. In this example, a direction ofdischarging the gas is the opposite a direction in which the turntable201 is rotated. An example of the decomposition accelerating gas mayinclude a gas containing B₂H₆ of 0.1% An example of processingconditions in the first processing stage PS1 may be that a flow rate ofthe gas containing B₂H₆ of 0.1% is 250 sccm and a processing pressure is133 Pa (1 Torr).

A processing stage adjacent to the processing stage PS1 in thecounterclockwise direction is the second processing stage PS2 in whichstep S2 shown in FIG. 7 is performed. The second processing stage PS2has a relatively narrow space. The silicon substrate 1 is exposed in thenarrow space while being mounted on the turntable 201. A gas supply pipe203 b is installed to supply an inert gas into the narrow space where apurging process is performed. The narrow space may serve as a gasseparation area where different process gases are separated. An exampleof the inert gas may be a nitrogen gas. The nitrogen gas is supplied ata flow rate of, e.g., 1000 sccm.

A processing stage adjacent to the second processing stage PS2 in thecounterclockwise direction is the third processing stage PS3 in whichstep S1 shown in FIG. 7 is performed. In the third processing stage PS3,a silicon source gas is supplied toward the surface to be processed ofeach of the silicon substrates 1. A gas supply pipe 203 c through whichthe silicon source gas is supplied, is disposed at an upper side of thethird processing stage PS3. The silicon source gas supplied from the gassupply pipe 203 c is applied toward the surface to be processed of eachof the silicon substrates 1 which is exposed in the third processingstage PS3 while being mounted on the turntable 201. At a portion nearthe second processing stage PS2 in the third processing stage PS3 of theprocessing chamber 202, an exhaust vent 204 b through which the siliconsource gas is discharged. An example of the silicon source gas may be aSi₂H₆ gas. An example of processing conditions in the third processingstage PS3 may be that a flow rate of the Si₂H₆ gas is 200 sccm and anprocessing pressure is 133 Pa (1 Torr).

A processing stage adjacent to the third processing stage PS3 in thecounterclockwise direction is the fourth processing stage PS4 where stepS4 shown in FIG. 7 is performed. The fourth processing stage PS4 has arelatively narrow space like the second processing stage PS2 and alsoserves as the gas separation area. A gas supply pipe 203 d is installedto supply an inert gas into the narrow space where the siliconsubstrates 1 are subjected to the purging process. An example of theinert gas may be a nitrogen gas. The nitrogen gas is supplied at a flowrate of, e.g., 1000 sccm.

A processing stage adjacent to the fourth processing stage PS4 in thecounterclockwise direction is the fifth processing stage PS5 where stepS6 shown in FIG. 7 is performed. In the fifth processing stage PS5, anitriding gas is supplied toward the surface to be processed of thesilicon substrate 1 and the supplied nitriding gas is changed to plasma.To do this, a gas supply pipe 203 e through which the nitriding gas issupplied and a plasma generation mechanism 205 is disposed at an upperside of the fifth processing stage PS5. The nitriding gas supplied fromthe gas supply pipe 203 e is applied toward the surface to be processedof the silicon substrate 1 which is exposed in the fifth processingstage PS5 while being mounted on the turntable 201. The plasmageneration mechanism 205 applies energy to the nitriding gas to generateat least active nitrogen. At a portion close to the fourth processingstage PS4 in the processing stage PS5 of the processing chamber 202, anexhaust vent 204 c is formed to discharge the nitriding gas. An exampleof the nitriding gas may be a nitrogen gas. In the ignition of theplasma, the nitrogen gas is supplied at a flow rate of 200 sccm and anargon gas is supplied at a flow rate of 4500 sccm. After the ignition,the supply flow rate of the nitrogen gas is changed to 5000 sccm.

Further, the fifth processing stage PS5 also serves as aloading/unloading stage in which the silicon substrate 1 is loaded intothe processing chamber 202 or unloaded from the processing chamber 202.The silicon substrate 1 is loaded into or unloaded from the processingchamber 202 through a wafer loading/unloading port 206. Theloading/unloading port 206 is opened and closed by a gate valve 207.

A processing stage adjacent to the fifth processing stage PS5 in thecounterclockwise direction is the sixth processing stage PS6 where stepS7 shown in FIG. 7 is performed. The sixth processing stage PS6 has arelatively narrow space like the second and fourth processing stages PS2and PS4 and also serves as the gas separation area. An inert gas issupplied into the narrow space through a gas supply pipe 203 f such thatthe silicon substrate 1 exposed to the narrow space is subjected to thepurging process.

A processing stage adjacent to the sixth processing stage PS6 in thecounterclockwise direction is the first processing stage PS1 asdescribed above. Thus, after the turntable 201 rotates once, the siliconsubstrates 1 mounted on the turntable 201 are subjected to the processesrelated to the sequence of steps S3→S2→S1→S4→S6→S7→S3, . . . as shown inFIG. 7. The exhaust vent 204 a of the first processing stage PS1 isinstalled at a portion close to the sixth processing stage PS6 in thefirst processing stage PS1 of the processing chamber 202.

In the film forming apparatus 200 configured as above, upon one rotationof the silicon substrate 1, the one cycle including the silicon filmforming process and the silicon film nitridation process as shown inFIG. 7 is completed. In the film forming apparatus 200, the turntable201 rotates the m number of times as the predetermined set value withthe silicon substrates 1 mounted thereon, thus forming the siliconnitride film on the surface to be processed of each of the siliconsubstrates 1.

Further, in the film forming apparatus 200 shown in FIG. 10, thepredetermined set value n in the silicon film forming process (thesequence of steps S3→S2→S1→S4) is “1” and similarly, the predeterminedset value p in the silicon film nitridation process (the sequence ofsteps S6→S7) is “1”. As a result, strictly speaking, as shown in FIG.11, the film forming apparatus 200 is operated to exclude thedetermination processes of both steps S5 and S8 from the sequence shownin FIG. 7. That is, in the silicon nitride film forming method accordingto the second embodiment, for “n=1” and “p=1”, whether the silicon filmforming process has been performed by the predetermined set value n(step S5) and whether the silicon film nitridation process has beenperformed by the predetermined set value p (step S8) may be omitted.

Accordingly, it is possible to perform the silicon nitride film formingmethod according to the first and second embodiments of the presentdisclosure using the horizontal batch-type film forming apparatus 200shown in FIG. 10.

<Dependency of Temperature on Film Thickness in Horizontal Batch-TypeFilm Forming Apparatus 200>

Hereinafter, the dependency of temperature on a thickness of the siliconnitride film formed using the horizontal batch-type film formingapparatus 200 will be described.

FIG. 12 is a view showing a relationship between the number of cyclesand thicknesses of the silicon nitride film at every processingtemperature. Further, the decomposition accelerating gas used in thefirst processing stage PS1 (step S3) is a diborane gas, the siliconsource gas used in the third processing stage PS3 (step S1) is amonosilane gas, and the nitriding gas used in the fifth processing stagePS5 (step S6) is an ammonia gas. Also, the number of revolutions of theturntable 201 was set to 2 rpm.

As shown in FIG. 12, in the film forming apparatus 200, a processingtemperature was changed to 450 degrees C., 400 degrees C., 350 degreesC., and 300 degrees C. As a result, it was confirmed that the siliconnitride film is formed even at the processing temperature of 300 degreesC. A film formation rate was increased as the processing temperatureincreases, and thus, a silicon nitride film having a greater thicknesswas formed at a smaller number of cycles.

As an example, in order to form a silicon nitride film having athickness of about 40 nm, about 150 cycles was required at theprocessing temperature of 450 degrees C. and about 350 cycles wasrequired at the processing temperature of 400 degrees C. In order toform a silicon nitride film having a thickness of about 20 nm, about 100cycles was required at the processing temperature of 450 degrees C.,about 160 cycles was required at the processing temperature of about 400degrees C., and about 400 cycles was required at the processingtemperature of about 350 degrees C. Also, in order to form a siliconnitride film having a thickness of about 10 nm, about 50 cycles wasrequired at the processing temperature of 450 degrees C., about 90cycles was required at the processing temperature of about 400 degreesC., about 200 cycles was required at the processing temperature of about350 degrees C., and about 330 cycles was required at the processingtemperature of about 300 degrees C.

As can be seen from the results, the formation of the silicon nitridefilm having a great thickness with better throughput requires selectinga high processing temperature, for example, ranging from 400 degrees C.to 450 degrees C. In addition, the formation of the silicon nitride filmhaving a small thickness requires selecting a processing temperatureranging from 300 degrees C. to 400 degrees C.

Further, in FIG. 12, in-plane uniformity of the thickness of the formedsilicon nitride film is indicated by numbers. For the processingtemperature of 450 degrees C. and the film thickness of about 40 nm, thein-plane uniformity was 42.58 (±%). For the processing temperature of400 degrees C. and the film thickness of about 40 nm, the in-planeuniformity was 39.21 (±%). However, for the processing temperature of400 degrees C. and a film thickness of about 28 nm, the in-planeuniformity was 31.84 (±%), thus obtaining a relatively good result.

Also, for the processing temperature of 350 degrees C., the in-planeuniformity was 29.81 (±%) when a film thickness is about 25 nm, and thein-plane uniformity was 29.75 (±%) when the film thickness is about 9nm, thus obtaining good results of less than 30 (±%). Also, for theprocessing temperature of 300 degrees C., the in-plane uniformity was41.35 (±%) when a film thickness is about 5 nm.

As can be seen from the above results, in order to obtain the in-planeuniformity of about 30 (±%) or lower in the thickness of the siliconnitride film, the processing temperature may be fallen within a range of300 degrees C. to 400 degrees C.

<Film Quality of Silicon Nitride Film in Film Forming Apparatus 200>

Hereinafter, a film quality of the silicon nitride film formed using thehorizontal batch-type film forming apparatus 200 will be described.

FIG. 13 is a view showing a relationship between a processingtemperature and a refractive index of the silicon nitride film. Therefractive index when a wavelength of light is about 632 nm isrepresented.

As shown in FIG. 13, the refractive index of the formed silicon nitridefilm ranges from 1.90 to 1.97 at a range of the processing temperatureof 300 degrees C. to 450 degrees C. This relationship shown that thesilicon nitride film formed using the horizontal batch-type film formingapparatus 200 has good film quality.

As described above, the silicon nitride film forming method according tothe above embodiments of the present disclosure can be sufficientlyperformed even by using the horizontal batch-type film forming apparatus200 as shown in FIG. 10.

<Modified Examples of Horizontal Batch-Type Film Forming Apparatus>

Hereinafter, modified examples of the horizontal batch-type film formingapparatus will be described.

FIG. 14A is a view showing a processing stage in a horizontal batch-typefilm forming apparatus 200 a according to a first modified example, FIG.14B is a view showing a processing stage in another horizontalbatch-type film forming apparatus 200 b according to a second modifiedexample, and FIG. 14C is a view showing a processing stage in anotherhorizontal batch-type film forming apparatus 200 c according to a thirdmodified example.

As shown in FIG. 14A, in the horizontal batch-type film formingapparatus 200 a, the interior of the processing chamber 202 is dividedinto six processing stages PS1 to PS6. Once the turntable 201 rotatesone time, the one cycle including the silicon film forming process (thesequence of steps S3→S2→S1→S4) and the silicon film nitridation process(the sequence of steps S6→S7) is carried out. That is, in the horizontalbatch-type film forming apparatus 200, one rotation of the turntable 201corresponds to the one cycle.

Meanwhile, in the horizontal batch-type film forming apparatus 200 bshown in FIG. 14B, the interior of the processing chamber 202 is dividedinto 12 processing stages (PS1 to PS12) such that the first to seventhprocessing stages PS1 to PS7 are repeated twice, compared with thehorizontal batch-type film forming apparatus 200 a shown in FIG. 14A.That is, in the horizontal batch-type film forming apparatus 200 b, onerotation of the turntable 201 corresponds to 2 cycles.

As described above, the processing stages in the processing chamber 202may be divided such that a plurality of cycles is carried out when theturntable 201 makes one rotation.

Further, in the horizontal batch-type film forming apparatus 200 c shownin FIG. 14C, the fifth and sixth processing stages PS5 and PS6 areomitted once, compared with the horizontal batch-type film formingapparatus 200 b shown in FIG. 14B. That is, the interior of theprocessing chamber 202 is divided into 10 processing stages PS1 to PS4and PS7 to PS12. When the processing stages are divided in this manner,the predetermined set value n in the silicon film forming process shownin FIG. 7 is set to “2.”

In this way, the processing stages of the processing chamber 202 may bedivided such that a plurality of silicon film forming processes and asingle silicon film nitridation process are performed when the turntable201 makes one rotation.

As described above, according to the first and second embodiments of thepresent disclosure, it is possible to provide the silicon nitride filmforming method capable of enhancing productivity of a film formingapparatus, while satisfying user demands such as film uniformity, andelectrical or physical characteristics and processability, withoutrelying only on hardware improvement, and the film forming apparatusconfigured to perform the film forming method.

While the present disclosure has been described according to the firstand second embodiments, the present disclosure is not limited thereto. Avariety of modifications may be made without departing from the spiritof the disclosures.

In the first and second embodiments, the specific processing conditionshave been described, but are not limited thereto. Alternatively, theprocessing conditions may be arbitrarily changed depending on a volumeof the processing chamber 101 or the like.

Further, while in the first and second embodiments, the film formingprocess has been described to be performed using the batch-type filmforming apparatus, a single-sheet type film forming apparatus may beused therefor. Also, the batch-type film forming apparatus is notlimited to the vertical one, but may be a horizontal batch-type filmforming apparatus.

According to the present disclosure in some embodiments, it is possibleto provide a silicon nitride film forming method capable of enhancingproductivity of a film forming apparatus, while satisfying user demandssuch as film uniformity, and electrical or physical characteristics andprocessability, without relying only on hardware improvement, and a filmforming apparatus configured to perform the film forming method.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosures. Indeed, the embodiments described herein maybe embodied in a variety of other forms. Furthermore, various omissions,substitutions and changes in the form of the embodiments describedherein may be made without departing from the spirit of the disclosures.The accompanying claims and their equivalents are intended to cover suchforms or modifications as would fall within the scope and spirit of thedisclosures.

What is claimed is:
 1. A method of forming a silicon nitride film on asurface to be processed of a target object, the method comprising:repeating a first process a first predetermined number of times, theprocess including supplying a silicon source gas containing silicontoward the surface to be processed and supplying a decompositionaccelerating gas containing a material for accelerating decomposition ofthe silicon source gas toward the surface to be processed; performing asecond process of supplying a nitriding gas containing nitrogen towardthe surface to be processed a second predetermine number of times; andperforming one cycle a third predetermined number of times, the onecycle being a sequence including the repetition of the first process andthe performance of the second process to form the silicon nitride filmon the surface to be processed.
 2. A method of forming a silicon nitridefilm on a surface to be processed of a target object, the methodcomprising: supplying a decomposition accelerating gas toward thesurface to be processed, and supplying a silicon source gas containingsilicon toward the surface to be processed, the decompositionaccelerating gas containing a material for accelerating decomposition ofthe silicon source gas; supplying a nitriding gas containing nitrogentoward the surface to be processed; and performing one cycle apredetermined number of times, the one cycle being a sequence includingthe supply of the decomposition accelerating gas and the silicon sourcegas and the supply of the nitriding gas to form the silicon nitride filmon the surface to be processed.
 3. The method of claim 1, whereinrepeating a first process is performed at a temperature ranging from anadsorption initiation temperature at which the adsorption of the silicononto the surface to be processed initiates to a chemical mechanicaldeposition (CVD) growth initiation temperature at which a CVD growth ofthe silicon initiates.
 4. The method of claim 3, wherein repeating afirst process is performed at a temperature ranging from 100 degrees C.to 400 degrees C.
 5. The method of claim 1, wherein repeating a firstprocess is performed at a temperature ranging from an adsorptioninitiation temperature at which the adsorption of the silicon onto thesurface to be processed initiates to a CVD growth transition initiationtemperature at which a transition of the silicon to a CVD growthinitiates.
 6. The method of claim 5, wherein repeating a first processis performed by the adsorption of the silicon.
 7. The method of claim 5,wherein repeating a first process is performed at a temperature rangingfrom 100 degrees C. to than 300 degrees C.
 8. The method of claim 1,wherein the decomposition accelerating gas contains none of a halogenelement.
 9. The method of claim 1, wherein the material for acceleratingdecomposition of the silicon source gas includes boron.
 10. The methodof claim 9, wherein the decomposition accelerating gas includes aborane-based gas.
 11. The method of claim 9, wherein the silicon nitridefilm is formed by supplying the decomposition accelerating gas in whicha content of the boron contained in the formed silicon nitride film isless than 1%, toward the surface to be processed.
 12. The method ofclaim 9, wherein the silicon nitride film is formed as aboron-containing silicon nitride film, by supplying the decompositionaccelerating gas in which a content of the boron contained in the formedsilicon nitride film is 1% or more, toward the surface to be processed.13. The method of claim 1, wherein the silicon source gas contains nohalogen element.
 14. The method of claim 1, wherein the silicon sourcegas includes a silane-based gas.
 15. The method of claim 1, whereinrepeating a first process and performing a second process are performedat the same temperature.
 16. The method of claim 1, further comprising:applying energy to the nitriding gas to generate an active nitrogen; andsupplying the active nitrogen toward the surface to be processed.
 17. Anapparatus of forming a silicon nitride film on a surface to be processedof a target object, comprising: a processing chamber configured toperform a film forming process on the target object; a silicon sourcegas supply mechanism configured to supply a silicon source gas into theprocessing chamber; a decomposition accelerating gas supply mechanismconfigured to supply a decomposition accelerating gas into theprocessing chamber; a nitriding gas supply mechanism configured tosupply a nitriding gas into the processing chamber; and a heating unitconfigured to heat the processing chamber; and a control unit configuredto control the silicon source gas supply mechanism, the decompositionaccelerating gas supply mechanism, the nitriding gas supply mechanism,and the heating unit such that the silicon nitride film forming methodof claim 1 is performed.
 18. The apparatus of claim 17, furthercomprising an energy application mechanism configured to apply energy tothe nitriding gas to generate at least a nitrogen radical, wherein thecontrol unit controls the energy applying mechanism such that thesilicon nitride film forming method of claim 16 is performed.
 19. Theapparatus of claim 17, wherein a plurality of target objects includingthe target object is received in the processing chamber in a heightdirection.
 20. The apparatus of claim 17, wherein a plurality of targetobjects including the target object is received in the processingchamber in a state where the plurality of target objects are mounted ona rotatable turntable in a circumferential direction, wherein theinterior of the processing chamber is divided into a plurality ofprocessing stages such that the silicon nitride film forming method ofclaim 1 is performed.
 21. The apparatus of claim 18, wherein a pluralityof target objects including the target object is received in theprocessing chamber in a state where the plurality of target objects aremounted on a rotatable turntable in a circumferential direction, whereinthe interior of the processing chamber is divided into a plurality ofprocessing stages such that the silicon nitride film forming method ofclaim 16 is performed.